A universal mobile telecommunication system (UMTS) is a European-type, third generation IMT-2000 mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM).
UMTS is intended to provide an improved mobile communication service based upon a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology. In December 1998, a Third Generation Partnership Project (3GPP) was formed by the ETSI of Europe, the ARIB/TTC of Japan, the T1 of the United States, and the TTA of Korea. The 3GPP creates detailed specifications of UMTS technology.
In order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created within the 3GPP for standardizing the UMTS by considering the independent nature of the network elements and their operations. Each TSG develops, approves, and manages the standard specification within a related region. The radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 provides an overview of a UMTS network. The UMTS network includes a mobile terminal or user equipment (UE) 1, a UTRAN 2 and a core network (CN) 3.
The UTRAN 2 includes several radio network controllers (RNCs) 4 and NodeBs (NB) 5 that are connected via the Iub interface. Each RNC 4 controls several NBs (NB) 5. Each NB controls one or several cells, where a cell covers a given geo-graphical area on a given frequency.
Each RNC 4 is connected via the Iu interface to the CN 3 or towards the mobile switching center (MSC) 6 entity of the CN and the general packet radio service (GPRS) support Node (SGSN) 7 entity. RNCs 4 can be connected to other RNCs via the Iur interface. The RNC 4 handles the assignment and management of radio resources and operates as an access point with respect to the CN 3.
The NBs 5 receive information sent by the physical layer of the UE 1 via an uplink and transmit data to the UE 1 via a downlink. The Node-Bs 5 operate as access points of the UTRAN 2 for the UE 1.
The SGSN 7 is connected to the equipment identity register (EIR) 8 via the Gf interface, to the MSC 6 via the GS interface, to the gateway GPRS support node (GGSN) 9 via the GN interface, and to the home subscriber server (HSS) via the GR interface.
The EIR 8 hosts lists of UEs 1 that are allowed access to the network. The EIR 8 also hosts lists of UEs 1 that are not allowed access to the network.
The MSC 6, which controls the connection for circuit switched (CS) services, is connected towards the media gateway (MGW) 11 via the NB interface, towards the EIR 8 via the F interface, and towards the HSS 10 via the D interface.
The MGW 11 is connected towards the HSS 10 via the C interface and also to the public switched telephone network (PSTN). The MGW 11 also allows the codecs to adapt between the PSTN and the connected RAN.
The GGSN 9 is connected to the HSS 10 via the GC interface and to the Internet via the GI interface. The GGSN 9 is responsible for routing, charging and separation of data flows into different radio access bearers (RABs). The HSS 10 handles the subscription data of users.
The UTRAN 2 constructs and maintains an RAB for communication between a UE 1 and the CN 3. The CN 3 requests end-to-end quality of service (QoS) requirements from the RAB and the RAB supports the QoS requirements set by the CN 3. Accordingly, the UTRAN 2 can satisfy the end-to-end QoS requirements by constructing and maintaining the RAB.
The services provided to a specific UE 1 are roughly divided into CS services and packet switched (PS) services. For example, a general voice conversation service is a CS service and a Web browsing service via an Internet connection is classified as a PS service.
The RNCs 4 are connected to the MSC 6 of the CN 3 and the MSC is connected to the gateway MSC (GMSC) that manages the connection with other networks in order to support CS services. The RNCs 4 are connected to the SGSN 7 and the gateway GGSN 9 of the CN 3 to support PS services.
The SGSN 7 supports packet communications with the RNCs. The GGSN 9 manages the connection with other packet switched networks, such as the Internet.
FIG. 2 illustrates a structure of a radio interface protocol between a UE 1 and the UTRAN 2 according to the 3GPP radio access network standards. As illustrated In FIG. 2, the radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane (U-plane) for transmitting user data and a control plane (C-plane) for transmitting control information. The U-plane is a region that handles traffic information with the user, such as voice or Internet protocol (IP) packets. The C-plane is a region that handles control information for an interface with a network as well as maintenance and management of a call. The protocol layers can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on the three lower layers of an open system interconnection (OSI) standard model.
The first layer (L1), or physical layer, provides an information transfer service to an upper layer by using various radio transmission techniques. The physical layer is connected to an upper layer, or medium access control (MAC) layer, via a transport channel. The MAC layer and the physical layer exchange data via the transport channel.
The second layer (L2) includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer. The MAC layer handles mapping between logical channels and transport channels and provides allocation of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to an upper layer, or the radio link control (RLC) layer, via a logical channel.
Various logical channels are provided according to the type of information transmitted. A control channel is generally used to transmit information of the C-plane and a traffic channel is used to transmit information of the U-plane. A logical channel may be a common channel or a dedicated channel depending on whether the logical channel is shared.
FIG. 3 illustrates the different logical channels that exist. Logical channels include a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a common traffic channel (CTCH), a common control channel (CCCH), a broadcast control channel (BCCH), and a paging control channel (PCCH), or a Shared Control Channel (SCCH), as well as other channels. The BCCH provides information including information utilized by a UE 1 to access a system. The PCCH is used by the UTRAN 2 to access a UE 1.
Additional traffic and control channels are introduced in the Multimedia Broadcast Multicast Service (MBMS) standard for the purposes of MBMS. The MBMS point-to-multipoint control channel (MCCH) is used for transmission of MBMS control information. The MBMS point-to-multipoint traffic channel (MTCH) is used for transmitting MBMS service data. The MBMS scheduling channel (MSCH) is used to transmit scheduling information.
The MAC layer is connected to the physical layer by transport channels. The MAC layer can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, a MAC-hs sub-layer and a MAC-m sublayer according to the type of transport channel being managed.
The MAC-b sub-layer manages a broadcast channel (BCH), which is a transport channel handling the broadcasting of system information. The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH) or a downlink shared channel (DSCH), which is shared by a plurality of UEs 1, or in the uplink the radio access channel (RACH). The MAC-m sublayer may handle MBMS data.
FIG. 4 illustrates the possible mapping between the logical channels and the transport channels from a UE 1 perspective. FIG. 5 illustrates the possible mapping between the logical channels and the transport channels from a UTRAN 2 perspective.
The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific UE 1. The MAC-d sublayer is located in a serving RNC 4 (SRNC) that manages a corresponding UE 1. One MAC-d sublayer also exists in each UE 1.
The RLC layer supports reliable data transmissions and performs segmentation and concatenation on a plurality of RLC service data units (SDUs) delivered from an upper layer depending of the RLC mode of operation. The RLC layer adjusts the size of each RLC SDU received from the upper layer in an appropriate manner based upon processing capacity and then creates data units by adding header information RLC SDU. The data units, or protocol data units (PDUs), are transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
An RLC entity may operate in one of three different modes. Specifically, an RLC entity may operate in a transparent mode (Tr RLC), an unacknowledged mode (UM RLC) or an acknowledged mode (AM RLC).
The differences between the three modes are whether or not a header will be added to one SDU and the three modes allow different functions with common segmentation and concatenation functions for. The RLC mode is according to the required radio bearer and the type of service, such as voice, video conferencing, VoIP, or Internet browsing.
The BMC layer schedules a cell broadcast (CB) message transferred from the CN 3. The BMC layer broadcasts the CB message to UEs 1 positioned in a specific cell or cells.
The PDCP layer is located above the RLC layer. The PDCP layer is used to transmit network protocol data, such as the IPv4 or IPv6, efficiently on a radio interface with a relatively small bandwidth. The PDCP layer reduces unnecessary control information used in a wired network, a function called header compression, for this purpose.
The PDCP layer may operate in one of three different modes depending upon whether or not IP header compression is performed. A PDCP header is added when IP header compression is performed. The header includes information such as header compression protocol type, packet type, and PDU type to indicate a data PDU or sequence number PDU.
A UE 1 must know which configuration, such as RLC mode or PDCP mode, to use in order for a given a Public Land Mobile Network (PLMN) to establish a connection with a specific radio bearer. This will be further disclosed with in relation to the radio bearer establishment procedure in UMTS.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the C-plane. The RRC layer controls the transport channels and the physical channels in relation to setup, reconfiguration, and the release or cancellation of the radio bearers (RBs).
A RB signifies a service provided by the second layer (L2) for data transmission between a UE 1 and the UTRAN 2. The set up of the RB generally refers to the process of stipulating the characteristics of a protocol layer and a channel required for providing a specific data service and setting the respective detailed parameters and operation methods. The RRC also handles user mobility within the RAN and additional services, such as location services.
Not all different possibilities for the mapping between the RBs and the transport channels for a given UE 1 are available all the time. The UE 1/UTRAN 2 deduce the possible mapping depending on the UE state and the procedure presently executed by the UE/UTRAN.
The different transport channels are mapped onto different physical channels. The configuration of the physical channels is given by RRC signaling exchanged between the RNC 4 and the UE 1.
Initial access is a procedure whereby a UE 1 sends a first message to the UTRAN 2 using a common uplink channel, specifically the Random Access Channel (RACH). For both GSM and UMTS systems, the initial access procedure involves the UE 1 transmitting a connection request message that includes a reason for the request and receiving a response from the UTRAN 2 indicating the allocation of radio resources for the requested reason.
There are several reasons, or establishment causes, for sending a connection request message. Table I indicates the establishment causes specified in UMTS, specifically in 3GPP TS 25.331.
The originating call establishment cause indicates that the UE 1 wants to setup a connection, for example, a speech connection. The terminating call establishment cause indicates that UE 1 answers to paging. The registration establishment cause indicates that the user wants to register only to location update.
A physical random access procedure is used to send information over the air. The physical random access transmission is under control of a higher layer protocol, which performs important functions related to priority and load control. This procedure differs between GSM and UMTS radio systems.
The description of GSM random access procedure can be found in The GSM System for Mobile Communications published by M. Mouly and M. B. Pautet, 1992. As the present invention is related to UMTS enhancement and evolution, the W-CDMA random access procedure is detailed herein. Although the present invention is explained in the context of UMTS evolution, the present invention is not so limited.
TABLE 1Establishment CausesOriginating Conversational CallOriginating Streaming CallOriginating Interactive CallOriginating Background CallOriginating Subscribed traffic CallTerminating Conversational CallTerminating Streaming CallTerminating Interactive CallTerminating Background CallEmergency CallInter-RAT cell re-selectionInter-RAT cell change orderRegistrationDetachOriginating High Priority SignalingOriginating Low Priority SignalingCall re-establishmentTerminating High Priority SignalingTerminating Low Priority Signaling
The transport channel RACH and two physical channels, Physical Random Access Channel (PRACH) and Acquisition Indication Channel (AICH), are utilized in this procedure. The transport channels are channels supplied by the physical layer to the protocol layer of the MAC layer. There are several types of transport channels to transmit data with different properties and transmission formats over the physical layer.
Physical channels are identified by code and frequency in Frequency Division Duplex (FDD) mode and are generally based on a layer configuration of radio frames and timeslots. The form of radio frames and timeslots depends on the symbol rate of the physical channel.
A radio frame is the minimum unit in the decoding process, consisting of 15 time slots. A time slot is the minimum unit in the Layer 1 bit sequence. Therefore, the number of bits that can be accommodated in one time slot depends on the physical channel.
The transport channel RACH is an uplink common channel used for transmitting control information and user data. The transport channel RACH is utilized in random access and used for low-rate data transmissions from a higher layer. The RACH is mapped to an uplink physical channel, specifically the PRACH. The AICH is a downlink common channel, which exists as a pair with PRACH used for random access control.
The E-UTRA (Evolved UMTS Terrestrial Radio Access) system, or LTE (Long Term Evolution) system, is considered to involve the PS (Packet Switched) domain with only shared resources used. The use of LTE RACH (LTE Random Access Channel) should be somewhat different from existing GSM and UMTS systems in order to meet access requirements specified for LTE with faster delay and higher capacity requirements. The E-UTRA and LTE are related to the principles of Orthogonal Frequency Division Multiplexing (OFDM).
FIG. 6 illustrates the architecture of an LTE system. Each aGW 115 is connected to one or several access Gateways (aGW) 115. An aGW 115 is connected to another Node (not shown) that allows access to the Internet and/or other networks, such as GSM, UMTS, and WLAN.
The 3G LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement. Generally, The UTRAN 2 corresponds to E-UTRAN (Evolved-UTRAN). The NB 5 and/or RNC 4 correspond to e-NodeB (eNb) in the LTE system.
OFDM is based on the well-known technique of Frequency Division Multiplexing (FDM). Different streams of information are mapped onto separate parallel frequency channels in FDM. Each FDM channel is separated from the other FDM channels by a frequency guard band in order to reduce interference between adjacent channels.
The OFDM technique differs from traditional FDM in the ways that multiple carriers, or sub-carriers, carry the information stream. The sub-carriers are orthogonal to each other in that the bandwidths of the individual sub-carriers are small and arranged such that the maximum of one carrier corresponds with the first minimum of the adjacent carrier. A guard time may be added to each symbol in order to address the channel delay spread.
An exemplary Frequency-Time representation of an OFDM signal may include multiple sub-carriers, with each sub-carrier having a particular bandwidth or frequency range. The signal may carry data or information represented by symbols with guard intervals between the symbols.
The multi-user system includes both uplinks and downlinks. The NB 5 measures the attenuation at the different uplink sub-carriers and distributes the sub-carriers according to the measurements for use by the different UEs 1 for uplink transmission. A UE 1 measures the attenuation for each downlink sub-carrier with the result of the measurement signaled to the NB 5, which distributes downlink sub-carriers for better UE reception.
A UE 1 transmits a known signal sequence, such as a specific coded signature, to the NB in a random access protocol. The UE 1 first listens for a pilot channel transmitted by the NB 5 and synchronizes to OFDM symbols transmitted by the NB 5 upon detection. The UE then listens to a broadcast system information channel for a random access sequence and a sub-carrier number assigned to a random access channel (RACH) and transmits a random access sequence in the random access channel. The UE 1 checks whether the NB 5 has granted access after transmission for a number of cycles of the random access sequence.
A UE 1 has to load a certain configuration when establishing a UMTS radio bearer service during radio bearer setup in each PLMN. The configuration includes RLC mode, PDCP mode, MAC configuration and other parameters that are used for the radio bearer.
The RNC will send the UE 1 the correct configuration for use upon establishment of a radio bearer. Different schemes are possible, from more efficient to less efficient.
The first scheme is a default configuration. The UE 1 has a set of configurations defined in the standard and stored in memory. Each configuration can be identified by a configuration identification (ID) and the NB 5 uses this ID to indicate to the UE 1 which configuration it should use. This configuration is called the default configuration.
The second scheme is a pre-defined configuration. A set of configurations currently used in the PLMN is broadcast on the System Information (SI). These configurations, which may be different from the default configurations, are called the pre-defined configurations and also are identified with a configuration ID. Therefore, the UE 1 should store these pre-defined configurations when listening to the SI and delete the pre-defined after expiration of a timer, such as a 6-hour System Information Broadcasts (SIB) timer.
The third scheme is an explicit configuration. The RNC may send the explicit configurations to the UE 1.
The determination of which of the three schemes to use depends on the configuration that should be used and on the availability of default configurations, the predefined configurations and the explicit configurations. All the pre-defined configurations either have an independent identifier or the configurations may be classified by set, with each set having a set ID and each configuration identified with a set ID and an index indicating a configuration within the identified set.
FIG. 7 illustrates an example message flow for radio bearer setup. The following description related to FIG. 7 assumes that each default configuration and pre-defined configuration has a unique configuration ID.
As illustrated in FIG. 7, a set of default configurations defined in the standard is stored in the UE 1 (S100). Each configuration has a unique configuration identifier.
A set of pre-defined configurations is broadcast in each cell of the PLMN. The UE 1 will listen to the SI upon moving to a different cell if the value tag on the SI has changed (S102). The UE 1 will store the pre-defined configurations for a specified time, such as six hours for the SIB timer expiration time.
The procedure performed by the UE 1 differs depending upon whether the UE is in an IDLE state or RRC connected state. The UE will perform step S104 through step S108 to transition to an RRC connected state in addition to step S110 through step S116 if in the IDLE state. The UE 1 will perform only step S110 through step S116 if already in RRC connected state.
A UE 1 in the IDLE state is requested by a higher layer to transition to RRC connected state. The UE 1 transmits an RRC connection request to the NB 5 along with the IDs of the pre-defined configuration the UE has stored in memory (S104). However, the NB 5 cannot know if the UE 1 successfully stored all the broadcasted pre-defined configurations.
The UE receives an RRC connection setup message from the NB 5 (S106). The RRC connection setup message indicates a configuration for the radio bearer used to setup an RRC connection and signaling. The configuration may be indicated by either sending the configuration ID of a default configuration or pre-defined configuration stored in the UE 1 or explicitly sending the configuration if the UE has not stored the required configuration.
The UE 1 then has established an RRC connection. The UE 1 then transmits an RRC connection setup complete message to the NB 5 (S108).
Default configurations as well as some pre-defined configurations are stored in the UE 1 once the UE is RRC connected (S110).
The UE 1 must send a UE capability information message to the NB 5 in order to inform the NB of the last pre-defined configuration stored in the UE if there is a change in the list of stored pre-defined configuration while an RRC connection is established (S112).
A radio bearer is then setup by the NB 5 informing the UE 1 of the configuration to use (S114). The NB 5 may inform the UE 1 of the configuration by either sending the configuration ID if the UE has stored the required default configuration or pre-defined configuration or explicitly sending the configuration if the UE has not stored the required configuration. The UE 1 then transmits a radio bearer setup complete message to the NB 5 (S116).
A UE 1 has to use a certain configuration compatible with the radio bearer that will be established during the radio bearer setup procedure in E-UTRAN. This configuration includes information such as RLC mode and PDCP mode.
There are different ways for a NB 5 in UMTS to indicate which configuration the UE 1 should use. The NB 5 can send the identifier of a default configuration stored in the UE 1, send the identifier of a configuration broadcast in a PLMN and temporarily stored in the UE, or send the exact configuration that the UE should use.